Apparatus and method for reducing peak to average power ratio in a signal

ABSTRACT

Methods and apparatuses for processing a signal that is transmitted with a reduced peak to average power ratio are described. The processing includes applying (1650) a symbol constellation extension projection to at least one symbol in the constellation, the symbol constellation extension projection having an outward angular region from an original position for the at least one symbol in the constellation, the outward angular region defined by a value for an angle between a first boundary and a second boundary for the outward angular region, the value for the angle determined by a selection of the constellation used as part of the transmitted signal and a code rate used for encoding the stream of data.

CROSS REFERENCE

This application is a continuation of U.S. application Ser. No.16/401,763, filed May 2, 2019, which is a continuation of U.S.application Ser. No. 15/569,610 filed Oct. 26, 2017, which claims thebenefit, under 35 U.S.C. § 365 of International ApplicationPCTEP2016/059538, filed Apr. 28, 2016, which claims priority to EP-EPA15305671.8, filed Apr. 30, 2015, which is herein incorporated byreference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present disclosure generally relates to communication systems. Moreparticularly, the present disclosure relates to peak to average powerratio reduction techniques used in a communication system.

BACKGROUND OF THE INVENTION

This section is intended to introduce the reader to various aspects ofart, which may be related to the present embodiments that are describedbelow. This discussion is believed to be helpful in providing the readerwith background information to facilitate a better understanding of thevarious aspects of the present disclosure. Accordingly, it should beunderstood that these statements are to be read in this light.

Many modern communication systems utilize multicarrier modulationtechniques, such as Orthogonal Frequency Division Multiplexing (OFDM).OFDM is a technique of encoding digital data on multiple carrierfrequencies. In OFDM, the sub-carrier frequencies are chosen so that thesub-carriers are orthogonal to each other, meaning that cross-talkbetween the sub-channels is eliminated and inter-carrier guard bands arenot required. This greatly simplifies the design of both the transmitterand the receiver; unlike conventional frequency division multiplexing(FDM), a separate filter for each sub-channel is not required. Theorthogonality allows for efficient modulator and demodulatorimplementation using the Fast Fourier Transform (FFT) algorithm on thereceiver side, and inverse FFT on the transmitter side. In particular,the size of the FFT identifies the number of carriers in the OFDMmodulation system. Frequency selective channels are characterized eitherby their delay spread or coherence bandwidth. In a single carriersystem, such as the eight level vestigial sideband (8-VSB) signaltransmission system, a single fade or interference can cause the wholelink to fail, but in multi-carrier systems, like OFDM, only a few of thetotal sub carriers will be affected. This way, multipath fading can beeasily eliminated in OFDM, with simpler equalization techniques than insingle carrier systems. OFDM is used in systems for terrestrialtelevision signal transmission (e.g., digital video broadcast standardsDVB-T and DVB-T2) as well as cellular telephone and wireless data signaltransmission, among others.

For the DVB-T2 system, there are several different FFT sizes to choosefrom, specifically, 1K, 2K, 4K, 8K, 16K, and 32K, where the number ofcarriers is equal to two to the N power that most closely equals thevalue indicated above in thousands. As the size of the FFT increases,the roll-off of the spectrum gets increasingly sharper. Normally, foreach FFT size, only a fixed number of the OFDM carriers are used and atthe edges of the spectrum, some of the carriers are not used to allowthe spectrum to roll-off enough to not interfere into the adjacentchannel. For the large FFT sizes (16K, 32K, etc.), the roll-off is verysharp allowing for some additional OFDM carriers to be utilized. Atthese higher FFT values, the DVB-T2 specification allows for either thenormal number of carriers or an extended number of carriers to be used.This is signaled to the receiver using the L1 pre-signaling data.

Further, each of the carriers may be modulated based on a modulationcode word set. The modulation depth or constellation pattern may varyfrom quadrature phase shift keying (QPSK) using two bit code words to256 level quadrature amplitude modulation (256-QAM) using 8 bit codewords.

OFDM modulation has been adopted for use in digital terrestrialtelevision standards, e.g., the DVB-T/DVB-T2 standards in Europe, andthe integrate services digital broadcast standard ISDB-T standard inJapan. DVB-T, the 1st generation of European Digital TerrestrialTelevision (DTT), is the most widely adopted and deployed standard.Since its publication in 1997, over 70 countries have deployed DVB-Tservices and 45 more have adopted (but not yet deployed) DVB-T. Thiswell-established standard benefits from massive economies of scale andvery low receiver prices. Like its predecessor, DVB-T2 uses OFDM(orthogonal frequency division multiplex) modulation with a large numberof sub-carriers delivering a robust signal, and offers a range ofdifferent modes, making it a very flexible standard. DVB-T2 uses thesame error correction coding as used in the DVB-S2 standard forsatellite signals and the DVB-C2 standard for cable signals: Low DensityParity Check (LDPC) coding combined with Bose-Chaudhuri-Hocquengham(BCH) coding, offering a very robust signal. The number of carriers,guard interval sizes and pilot signals can be adjusted, so that theoverheads can be optimized for any target transmission channel. DVB-T2offers more robustness, flexibility and at least 50% more efficiencythan any other DTT system. It supports standard definition (SD), highdefinition (HD), ultra high definition (UHD), mobile TV, or anycombination thereof.

OFDM has also been adopted in other wireless communication networks suchas, but not limited to, the Institute of Electrical and ElectronicsEngineers Standard IEEE 802.11 wireless standard, the cellular 3Gpartnership project long term evolution (3GPP LTE) standard, and thedigital audio broadcast (DAB) standard. OFDM has also been used in otherwired protocols including, but not limited to, multimedia over cablealliance (MoCA) system for coaxial cable, and the asymmetrical digitalsubscriber line (ADSL) and very high bit rate DSL (VDSL) system fortelephone lines. The attributes and parameters described above alsoapply equally to these OFDM implementations.

Recently, the Advanced Television Systems Committee (ATSC), whichproposes terrestrial broadcasting digital television standards in theU.S., announced a call for proposals for the next generation (named ATSC3.0) physical layer. ATSC 3.0 will provide even more services to theviewer and increased bandwidth efficiency and compression performance,which requires breaking backwards compatibility with the currentlydeployed version, ATSC A/53, which comprises an 8-VSB (8 level,Vestigial Sideband) modulation system. ATSC 3.0 is expected to emergewithin the next decade and it intends to support delivery to fixeddevices of content with video resolutions up to Ultra High Definitionhaving 3840 pixels by 2160 pixels at 60 frames per second (fps). ATSC3.0 may utilize many of the principles outlined above related to OFDMand may further include a plurality of signal modulation constellationpatterns. The intention of the system is to support delivery toportable, handheld and vehicular devices of content with videoresolution up to High Definition having 1920 pixels by 1080 pixels at60fps. The system is also expected to support lower video resolutionsand frame rates.

Despite its competitive attributes, however, OFDM signals have a majordisadvantage compared to single carrier signals: a high Peak-to-AveragePower Ratio (PAPR). When the OFDM signal is transformed to the timedomain, the resulting signal is the sum of all the sub-carriers, whichmay add up in phase, resulting in a signal peak up to N times higherthan the average signal power, where N is the number of sub-carriers.This characteristic leads the OFDM signals to be very sensitive tononlinearities of analog components of the transceiver, in particularthose of the High Power Amplifier (HPA) at the emission.

An HPA is conceived to operate in its saturation zone, which correspondsto its high efficiency region. However, in this zone, the HPA has asevere nonlinear behavior. These nonlinearities are sources of In-Band(IB) distortions which can both degrade the link performance in terms ofBit Error Rate (BER) and also cause significant Out-Of-Band (OOB)interference products that make it harder for the operator to complywith stringent spectral masks. The simplest solution to this problem isto operate the HPA in the linear region by allowing a large enoughamplifier back-off. However, this approach degrades the power efficiencyof the system and often leads to unacceptable cost-efficiency conditionsin the overall system. For all these reasons, reducing the PAPR of OFDMsignals is increasingly being considered to be very important inmaintaining the cost-effectiveness advantages of OFDM in practicalsystems, especially as new systems like DVB-T2 are being specified withlarge numbers of carriers (up to 32K and 256-QAM modulation).

Many techniques have been proposed to reduce PAPR values in OFDMsystems, but most of them either reduce the efficiency of thetransmission or deliberately degrade the quality of the transmittedsignal. For example, an Active Constellation Extension (ACE) mechanismhas been proposed as an efficient method to reduce the PAPR values inboth single input single output (SISO) and multiple input multipleoutput (MIMO) communication systems and have also been adopted for usewith DVB-T2 broadcast systems. However, these systems are not optimalfor all signal modulation constellation patterns. For example, ATSC 3.0is considering using two dimensional (2D) non-square constellationpatterns containing 16, 64, or 256 constellation symbols or points. TheACE mechanism works well with QAM modulated sub-carriers using squareconstellation because the boundary points of the square QAMconstellation are extended following the real or imaginary axisdirection. However, the ACE techniques as used with DVB-T2, as well assimilar PAPR reduction techniques, have very low efficiency fornon-square constellations proposed for ATSC 3.0.

When a new broadcast system is deployed, as it will eventually be thecase for ATSC 3.0, the new broadcast system may co-exist with theexisting system for some time. In addition, there is usually somechannel re-alignment involved where channels are moved around theavailable spectrum to accommodate both new and existing channels. Thisplanning process can be quite difficult as it must take into account theinterference between the various channels when planning where thechannels can be located. The co-existence condition highlights theimportance of considering PAPR reduction techniques one of thepriorities of the new system, particularly because of potential adjacentand co-channel interferences with the pre-existing single carriersystem. Therefore, there is a need for an improvement to the PAPRreduction techniques used in conjunction with OFDM systems based on newand different signal modulation constellation patterns, including theOFDM system for ATSC 3.0.

SUMMARY

According to an aspect of the present disclosure, a method processing astream of data converted into a plurality of symbols in a constellationas part of transmitting a signal is described The method includesapplying a symbol constellation extension projection to at least onesymbol in the constellation, the symbol constellation extensionprojection having an outward angular region from an original positionfor the at least one symbol in the constellation, the outward angularregion defined by a value for an angle between a first boundary and asecond boundary for the outward angular region, the value for the angledetermined by a selection of the constellation used as part of thetransmitted signal and a code rate used for encoding the stream of data.

According to another aspect of the present disclosure, an apparatusprocessing a stream of data converted into a plurality of symbols in aconstellation as part of transmitting a signal is described. Theapparatus includes a projection module (670), the projection moduleapplying a symbol constellation extension projection to at least onesymbol in the constellation, the symbol constellation extensionprojection having an outward angular region from an original positionfor the at least one symbol in the constellation, the outward angularregion defined by a value for an angle between a first boundary and asecond boundary for the outward angular region, the value for the angledetermined by a selection of the constellation used as part of thetransmitted signal and a code rate for used for encoding the stream ofdata.

According to a further embodiment, a method for processing a receivedsignal transmitted as a constellation of symbols representing a datastream that has been encoded using a code rate is described. The methodincludes demodulating the received signal to provide an estimation of atleast one symbol in the transmitted signal on an extended constellation,the extended constellation including at least one extended region formedas an outward angular sector from an original location for a symbol inthe constellation, the outward angular region defined by a value for anangle between a first boundary and a second boundary for the outwardangular region, the value for the angle determined by a selection of theconstellation used as part of the transmitted signal and the code ratefor the data stream in the signal.

According to yet another embodiment, an apparatus for processing areceived signal transmitted as a constellation of symbols representing adata stream that has been encoded using a code rate is described. Theapparatus includes a demodulator that demodulates the received signal toprovide an estimation of at least one symbol in the transmitted signalon an extended constellation, the extended constellation including atleast one extended region formed as an outward angular sector from anoriginal location for a symbol in the constellation, the outward angularregion defined by a value for an angle between a first boundary and asecond boundary for the outward angular region, the value for the angledetermined by a selection of the constellation used as part of thetransmitted signal and the code rate for the data stream in the signal.

The above presents a simplified summary of the subject matter in orderto provide a basic understanding of some aspects of subject matterembodiments. This summary is not an extensive overview of the subjectmatter. It is not intended to identify key/critical elements of theembodiments or to delineate the scope of the subject matter. Its solepurpose is to present some concepts of the subject matter in asimplified form as a prelude to the more detailed description that ispresented later.

BRIEF DESCRIPTION OF THE DRAWINGS

These, and other aspects, features and advantages of the presentdisclosure will be described or become apparent from the followingdetailed description of the preferred embodiments, which is to be readin connection with the accompanying drawings.

FIG. 1 illustrates a simplified block diagram of a general digitalcommunication system applicable to the digital broadcasting channelaccording to aspects of the present disclosure;

FIG. 2 illustrates a block diagram of an exemplary wireless networkaccording to aspects of the present disclosure;

FIG. 3 illustrates a block diagram of an exemplary transmitter sourceaccording to aspects of the present disclosure;

FIG. 4 illustrates a block diagram of an exemplary data receiveraccording to aspects of the present disclosure;

FIG. 5 illustrates a block diagram of another exemplary data transmitteraccording to aspects of the present disclosure;

FIG. 6 illustrates a block diagram of an exemplary pre-encoder used in adata transmitter according to aspects of the present disclosure;

FIG. 7 illustrates a block diagram of another exemplary pre-encoder usedin a data transmitter according to aspects of the present disclosure;

FIG. 8 shows a diagram for a 16-QAM square constellation applying PAPRtechniques according to aspects of the present disclosure;

FIG. 9 shows a diagram for a 16-QAM non-square constellation applyingPAPR techniques according to aspects of the present disclosure;

FIG. 10 shows a diagram for a 64-QAM non-square constellation applyingPAPR techniques according to aspects of the present disclosure;

FIG. 11 shows a diagram for a 64-QAM non-square constellation applyingimproved PAPR techniques according to aspects of the present disclosure;

FIG. 12 shows a diagram illustrating the application of the extensionmask to one point of the constellation with respect to different casesof the input signal of the projection block according to aspects of thepresent disclosure;

FIG. 13 shows a graph of performance of PAPR techniques for a 16-QAMnon-square constellation according to aspects of the present disclosure;

FIG. 14 shows a graph of performance of PAPR techniques for a 64-QAMnon-square constellation according to aspects of the present disclosure

FIG. 15 shows a graph of performance of PAPR techniques for a 256-QAMnon-square constellation according to aspects of the present disclosure;

FIG. 16 shows a flow chart of an exemplary process for reducing the PAPRin a signal according to aspects of the present disclosure;

FIG. 17 illustrates a block diagram of a further exemplary pre-encoderused in a data transmitter according to aspects of the presentdisclosure;

FIGS. 18A and 18B show a series of diagrams for a 16-QAM non-squareconstellation having different error correction code rates applying PAPRtechniques according to aspects of the present disclosure;

FIGS. 19A and 19B show a series of diagrams for a 64-QAM non-squareconstellation having different error correction code rates applying PAPRtechniques according to aspects of the present disclosure; and

FIG. 20 shows a series of diagrams for a 256-QAM non-squareconstellation having different error correction code rates applying PAPRtechniques according to aspects of the present disclosure.

It should be understood that the drawing(s) are for purposes ofillustrating the concepts of the disclosure and is not necessarily theonly possible configuration for illustrating the disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It should be understood that the elements shown in the figures may beimplemented in various forms of hardware, software or combinationsthereof. Preferably, these elements are implemented in a combination ofhardware and software on one or more appropriately programmedgeneral-purpose devices, which may include a processor, memory andinput/output interfaces. Herein, the phrase “coupled” is defined to meandirectly connected to or indirectly connected with through one or moreintermediate components. Such intermediate components may include bothhardware and software based components.

The present description illustrates the principles of the presentdisclosure. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of thedisclosure and are included within its scope.

All examples and conditional language recited herein are intended foreducational purposes to aid the reader in understanding the principlesof the disclosure and the concepts contributed by the inventor tofurthering the art, and are to be construed as being without limitationto such specifically recited examples and conditions.

Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosure, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat the block diagrams presented herein represent conceptual views ofillustrative circuitry embodying the principles of the disclosure.Similarly, it will be appreciated that any flow charts, flow diagrams,state transition diagrams, pseudocode, and the like represent variousprocesses which may be substantially represented in computer readablemedia and so executed by a computer or processor, whether or not suchcomputer or processor is explicitly shown.

The functions of the various elements shown in the figures may beprovided through the use of dedicated hardware as well as hardwarecapable of executing software in association with appropriate software.When provided by a processor, the functions may be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which may be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and mayimplicitly include, without limitation, digital signal processor (DSP)hardware, read only memory (ROM) for storing software, random accessmemory (RAM), and nonvolatile storage.

Other hardware, conventional and/or custom, may also be included.Similarly, any switches shown in the figures are conceptual only. Theirfunction may be carried out through the operation of program logic,through dedicated logic, through the interaction of program control anddedicated logic, or even manually, the particular technique beingselectable by the implementer as more specifically understood from thecontext.

In the claims hereof, any element expressed as a means for performing aspecified function is intended to encompass any way of performing thatfunction including, for example, a) a combination of circuit elementsthat performs that function or b) software in any form, including,therefore, firmware, microcode or the like, combined with appropriatecircuitry for executing that software to perform the function. Thedisclosure as defined by such claims resides in the fact that thefunctionalities provided by the various recited means are combined andbrought together in the manner which the claims call for. It is thusregarded that any means that can provide those functionalities areequivalent to those shown herein.

Described herein are mechanisms for coding of a stream of input datainto a constellation of symbols in order to reduce the PAPR for thesignal and also processing those symbols in a receiver to reduce orcompensate for the presence of the PAPR reduction in the receivedsignal. The mechanisms include mapping the stream of input data into aset of symbols, applying a constellation extension projection in aconstellation to at least one symbol, and modulating the processedsymbols to produce a transmitted signal, wherein the processing appliesa constellation extension projection to the at least one symbol in anoutward angular region, the outward angular region defined by a valuefor an angle between a first boundary and a second boundary for theoutward angular region. The value of the angle is determined through acombination of determining a type of constellation that will be used aswell as the signal coding rate that is used for the stream of data. Inother words, the angle is dependent on a selection of, or based on, thesymbol constellation that is used as part of transmitting the signal.Further, the angle is determined by adjusting the angle based on theamount of forward error correction (FEC) coding that is applied to thesignal. The angle determined and used in this manner is more optimal forPAPR reduction as described below. As a result, the value for the angleused to form, or bound, the outward angular region as part of reducingPAPR using an active constellation extension varies depending on thechoice of symbol constellation as well as the FEC code rate for the datastream in the signal.

The principles of the present disclosure enables a reduced PAPR in adata transmission over a wireless channel while maintaining reducedcomplexity in the encoders since the encoding process is not iterative.Reduced complexity is also important in the decoding process, especiallywhen used in a MIMO lattice decoder where the number of dimensionsbecomes large. The principles may be applied to many systems that arebased on multi-carrier transmission. The principles may further becompliant with many decoding methods including Maximum Likelihood (ML)or non ML decoding. The principles are most effective when applied toconstellations for the transmitted signal that are non-square. Theprinciples may also be effective when applied to constellations for thetransmitted signal that are non-uniform. Furthermore, the principles arecompliant to decoding of data transmitted through a Single Input SingleOutput (SISO), Multiple Input Single Output (MISO), or Multiple InputMultiple Output (MIMO) channel. Further, although the principles aredescribed for constellations having 16, 64, or 256 points, theprinciples may be applied to constellations having fewer or greaternumber of points, including, but not limited to 1,024 or 4,096 pointconstellations.

In the embodiments described herein, certain elements shown in thefigures are well known and will not be described in detail. For example,other than the inventive concept, familiarity with PAPR concepts andPAPR reduction techniques is assumed and not described herein in detail.Also, familiarity with the second generation digital terrestrialtelevision broadcasting system for DVB-T2 is assumed and not describedherein. In this regard, familiarity with the standards and recommendedpractices of the European Telecommunications Standards Institute (ETSI)Engineering Norm (EN) 302 755 and ETSI technical standard (TS) 102 832is assumed and not described herein. Additionally, familiarity withdigital terrestrial television broadcasting system for the US, referredto as ATSC, is assumed and not described herein. In this regard,familiarity with the standards and recommended practices of ATSCstandards A/53, A/153 and A/54 is assumed. Further, familiarity withother systems that may use OFDM techniques are assumed, including butnot limited to wireless data or phone networks and wired networks usinga copper or optical physical medium. It should also be noted that theinventive concept may be implemented using conventional programmingtechniques, which, as such, will not be described herein.

Turning now to FIG. 1, a simplified block diagram of a system 100 of ageneral digital communication system applicable to the digitalbroadcasting channel is shown. System 100 is shown as independent of themodulation system and system architecture. System 100 may be used, inwhole or in part, as part of a system for DVB-T2 or ATSC, or any othersimilar digital broadcasting system, for example, a digital terrestrialbroadcasting system including transmitter of a digital terrestrialbroadcast signal and receiver of a digital terrestrial.

System 100 includes a transmitter 110 connected to a receiver 120. Thetransmitter 110 includes the following components:

-   -   a source 111 that contains and/or provides audio, video,        signaling or control and other ancillary data (e.g., program        guide data);    -   a source encoder 112, connected to the source 111, including        audio and video encoders to compress the audio and video data;    -   a channel encoder 113, connected to the source encoder 112,        including at least some of the functions of randomizing,        interleaving, channel coding and frame mapping to process the        compressed, signaling and ancillary digital data for robustness        and to add levels of error correcting encoding functionality;    -   a modulator 114, connected to the channel encoder 113, that        converts the processed digital data into modulation symbols,        which can be, for example, VSB (ATSC) or OFDM (DVB-T2). In        addition, it includes the functionality of filtering and        digital-to-analog (D/A) conversion; and    -   an antenna 115, connected to the modulator 114, that includes        the functionalities for up-conversion, RF amplification and        over-the-air broadcasting.

Antenna 115 in transmitter 110 radiates a broadcast signal that isreceived by a receiver device 120.

At the receiver 120, the inverse functions of the transmitter 110 areperformed, including the following components:

-   -   an antenna/tuner 125, that includes the functionalities of        over-the-air reception, RF down-conversion and tuning;    -   a demodulator 124, connected to antenna/tuner 125, that recovers        the digital data from the modulation symbols and includes the        functionalities of analog-to-digital conversion (D/A), gain        control, carrier and symbol timing recovery, equalization and        header or preamble sync detection;    -   a channel decoder 123, connected to demodulator 124, that        recovers the compressed and ancillary data by performing the        inverse functionalities of the channel encoder, including error        correcting decoding, de-interleaving and de-randomizing;    -   a source decoder 122, connected to channel decoder 123, that        decompresses the audio and video data, including video and audio        decoders; and    -   a display device 121, connected to source decoder 122, for        audio/video viewing.

A skilled artisan will appreciate that a source encoder 112 and achannel encoder 113, although common in general communications systems,are not essential for a system according to the present principles.Similarly, depending on the transmitter, a source decoder 122 and achannel decoder 123, although common in general communications systems,are not essential for a system according to the present principles. Inaddition, the transmitter 110 and receiver 120 may not require anantenna, if the transmission system is other than over-the-air (e.g.,over cable). Furthermore, some receivers may not include a display 121.It is also important to note that several components andinterconnections necessary for complete operation of transmitter 110 andreceiver 120 are not shown in the interest of conciseness, as thecomponents not shown are well known to those skilled in the art.Exemplary receivers include, but are not limited to, televisions,set-top boxes, computers, gateways, mobile phones, mobile terminals,automobile radio receivers, and tablets.

Turning to FIG. 2, a block diagram of an exemplary wireless network 200is shown. Wireless network 200 includes two way communication betweendevices in the network and is shown as independent of the modulationsystem and system architecture. Wireless system 100 may use elementssimilar to those described in transmitter 110 and receiver 120 describedin FIG. 1. It is also important to note that several components andinterconnections necessary for complete operation of wireless networkare not shown in the interest of conciseness, as the components notshown are well known to those skilled in the art.

Wireless network 200 includes transceiver stations 210, 220, and 230.Each station 210, 220, and 230 comprises a transmitter and a receiverusing a MIMO antenna system. MIMO uses a plurality of antennas in thecommunication link for receiving and transmitting a signal. Each stationmay also employ a plurality of transmitter and receiver circuitsassociated with the plurality of antennas. Discussion of an exemplaryMIMO transmitter and receiver circuit will be described in detail below.Station 230 communicates using MIMO with stations 210 and 220 through awireless link.

Turning now to FIG. 3, a block diagram of an exemplary data transmitter300 capable of sending data in accordance with the principles of thepresent disclosure is shown. Data transmitter 300 may be implemented aspart of stations 210, 220, and 230 in order to communicate using MIMOtechniques described in FIG. 2. Further, portions of data transmitter300 may be incorporated into transmitter 110 described in FIG. 1. It isalso important to note that several components and interconnectionsnecessary for complete operation of transmitter 300 are not shown in theinterest of conciseness, as the components not shown are well known tothose skilled in the art.

The data transmitter 300 includes the following components:

-   -   a modulator 310 that receives an input data stream;    -   a pre-encoder 320 coupled to modulator 310;    -   a Space Time Block Code (STBC)/Space Frequency Block Code (SFBC)        encoder 330 coupled to pre-encoder 320;    -   OFDM modulators 340 and 350 each coupled to STBC/SFBC encoder        330; and    -   antennas 360 and 370, each being associated and coupled to an        OFDM modulator 340 and 350 respectively.

It is important to note that in the present embodiment antennas 360 and370 are considered as including Radio Frequency (RF) circuitry, such asfrequency transposition, power amplification and filtering.Advantageously, antennas 360 and 370 include a linearised HPA that isdesigned to mitigate distortion of the transmitted signal. Otherembodiments may include RF circuitry separate from the antennas.Further, data transmitter 300 shows only two OFDM modulators andantennas, however, other embodiments may include more than two and stillother embodiments, such as those intended for single input single output(SISO) operation, may include only one.

The data transmitter 300 receives a binary signal as part of a datastream. The binary signal is digitally modulated by the modulator 310using a first modulation format (e.g., 16 QAM or 64 QAM). The modulator310 generates groups of complex QAM symbols. The number of complex QAMsymbols in each group may, for example, be equal to 1024 and equals theproduct of the STBC/SFBC rate by the numbers of transmit antennas,identified as Ntx (e.g., two), and by the number of subcarriers. In oneembodiment, the code rate is equal to one, Ntx equals two and the numberof subcarriers equals 512.

Each group of complex QAM symbols may be pre-encoded according toprinciples of the present disclosure. In one embodiment, pre-encodingmay further include performing a transform on the group of QAM symbols,as a stream of data, to convert the group of QAM symbols to a transformor time domain signal. The amplitude of the transform domain signal islimited to produce a clipped transform signal. An inverse transform isperformed on the clipped transform signal to an inverse transform orfrequency domain signal again. The values or signal levels for theoriginal stream of data, or group of QAM symbols, are subtracted fromthe values or signal levels for the stream of data from the inversetransform signal to produce a remainder signal. The signal level of theremainder signal is adjusted, or multiplied by a pre-determined factor(e.g., a gain value K) to produce an adjusted remainder signal. Thevalues or signal levels for the original stream of data, or group of QAMsymbols are added to the values or signal levels for the adjustedremainder signal to produce an error signal. The error signal is used aspart of a constellation projection mapping for the original group of QAMsymbols. Other embodiments employing other pre-encoding techniques maybe used in place of the techniques described here. Details ofpre-encoding techniques will be described in further detail below.

After pre-encoding, each group of encoded symbols is further encoded toform a STBC/SFBC codeword STBC/SFBC encoder 330. The STBC/SFBC codewordmay be one of several known codeword structures. The STBC/SFBC codewordis typically based on a complex matrix of dimension N_(tx)*N where N isthe time dimension of the STBC/SFBC. In one embodiment, a codeword setknown as Golden code may be used.

At the output of STBC/SFBC encoder 330, the generated signal has beenmapped in a time/frequency mapping that provides a dedicated signal toeach of OFDM modulator 340 and 350. Each modulator 340 and 350 modulatesthe respective input signal into an OFDM modulated signal that is senton antennas 360 and 370 (after possibly filtering, frequencytransposition and amplification as usually done in a radio transmittedsignal). As a result, the information data received at the input of datatransmitter 300 is sent on a MIMO channel to a receiver in anotherdevice. According to present principles of the disclosure, the data maybe sent with a reduced PAPR using the embodiments described below.

Although FIG. 3 describes modulation using QAM, other modulationarrangements are possible. The first modulation in modulator 310 may beof any digital modulation, such as nPSK (i.e., PSK with n phase values)or nQAM (i.e., QAM with n equals to 16, 32, 64, 256 . . . ) and mayinclude non-square constellation patterns.

Turning to FIG. 4, a block diagram of an exemplary data receiver 400capable of receiving data in accordance with the principles of thepresent disclosure is shown. Data receiver 400 receives a signal send bya transmitter, such as data transmitter 300, through a wireless channel.This channel is noisy and comprises Additive White Gaussian Noise (AWGN)and possibly other noise, such as environmental interference. The sentsignal in the channel may also be affected by multipath echoes and/ordoppler effect. Data receiver 400 may be implemented as part of stations210, 220, and 230 in order to communicate using MIMO techniquesdescribed in FIG. 2. Further, portions of data receiver 400 may beincorporated into receiver 120 described in FIG. 1. It is also importantto note that several components and interconnections necessary forcomplete operation of data receiver 400 are not shown in the interest ofconciseness, as the components not shown are well known to those skilledin the art.

The data receiver 400 includes the following components:

-   -   antennas 410 and 420 that receive the transmitted signal;    -   OFDM demodulators 430 and 440 associated and coupled to antennas        410 and 410 respectively and each demodulating a noisy OFDM        modulated signal received by antennas 410 and 420;    -   a time/frequency demapper 450 coupled to both OFDM demodulator        430 and OFDM demodulator 440;    -   a decoder 460 coupled to time/frequency demapper 450; and    -   a demodulator 470 coupled to decoder 460 and providing a data        stream of information bits for further processing in a device.

The operation of data receiver 400 is intended for reception,demodulation, and decoding of a signal provided by a transmitter, suchas data transmitter 300 described in FIG. 3, especially with respect tomodulation and coding used as part of the signal transmission. Datareceiver 400 comprises receive antennas 410 and 420 so that the receivedsignal may be represented by a matrix that is two by two. As anextension for a set of antennas Nrx, the received signal may berepresented by an Nrx*N matrix or equivalently a (Nrx*N)*1 vector R. Nis, for instance, equal to two in the present embodiment, and representsthe time and/or frequency range occupied by the STBC.

The transmission between the pre-encoder 320 and decoder 460 can bemodeled by the following equation:

$\begin{matrix}{R = {{{\underset{\underset{G}{}}{\begin{pmatrix}H_{1} & 0 & \ldots & 0 \\0 & H_{2} & \ddots & \vdots \\\vdots & \ddots & \ddots & 0 \\0 & \ldots & 0 & H_{N}\end{pmatrix}}{CS}} + v} = {{GS} + v}}} & \left( {{equation}\mspace{14mu} 1} \right)\end{matrix}$

Where the different parameters are as follows:

-   R is the complex (Nrx*N)*1 received vector;-   H_(i) is the complex Nrx*Ntx channel matrix at time/frequency    interval i (frequency corresponds to a carrier of the multicarrier    modulation; according to a variant using a single carrier modulation    the interval i corresponds to a time interval);-   H=diag(H₁, . . . , H_(N)) is the complex block diagonal    (N*Nrx)*(N*Ntx) channel matrix at time/frequency intervals 1 to N;-   C is the complex (Ntx*N)*Q STBC/SFBC coding matrix (e.g. Q=4 or 8),    where Q is the number of input complex symbols per STBC/SFBC    codeword;-   S is the complex Q*1 input vector of extended modulated symbols    (after pre-encoding). CS in equation (1) denotes the STB encoded    signal. The encoding process is represented by complex matrix    multiplications;-   v is the complex (N*Nrx)*1 Additive White Gaussian Noise (or AWGN)    vector with autocorrelation matrix R_(v)=σ²INNrx, where INNrx is the    identity matrix of size (N*Nrx)*(N*Nrx) and σ² represents the    variance of the AWGN.

According to a variant, the space/time coding process takes place withreal inputs instead of complex inputs. In this variant, the C matrix isa real matrix with a dimension (2Ntx*1V)*(2Q).

When the additive noise and interferences corrupting the received signalis not white, a whitening filter is advantageously implemented beforethe decoder 460. σ² represents the variance of the resulting whitenednoise.

The time/frequency demapper 450 receives the OFDM demodulated signalsfrom OFDM demodulators 430 and 440 and is doing the reverse mapping(corresponding to dual operation of pre-encoder 330 in FIG. 3).Time/frequency demapper 450 provides a demapped signal to decoder 460.

The decoder 460 may be any decoder adapted to decode a signal that isbased on a coding such as implemented in a MIMO transmitter, such asdata transmitter 300 described in FIG. 3. According to a specificembodiment, the decoder 460 is a lattice decoder and is particularlywell suited to perform ML decoding of the STBC/SFBC encoded signal.

Advantageously, the decoder 460 is adapted to take into account thespecific characteristics and attributes of the pre-encoder 330 in FIG.3, and especially of a projection of the characteristics or attributesacross a constellation change. For example, if the signal provided tothe OFDM modulators 340 and 350 in FIG. 3 correspond to a signal with afirst constellation that is different than a second constellation usedby the modulator 310, then the decoder 460 is adapted to decode areceived signal corresponding to the first constellation.

The decoder 460 sends a decoded signal to demodulator 470. Thedemodulator 470 demodulates the decoded signal according to the mappingassociated to the second constellation and provides a demodulated signal(e.g. a series or stream of bits). In other terms, the demodulator 470associates a symbol of the second constellation to a decoded signal.

Turning now to FIG. 5, a block diagram of another exemplary datatransmitter 500 capable of sending data in accordance with theprinciples of the present disclosure is shown. Data transmitter 500 mayincorporate some or all of the elements of data transmitter 300described in FIG. 3. Data transmitter 500 may further be implemented aspart of stations 210, 220, and 230 in order to communicate using MIMOtechniques described in FIG. 2. Further, portions of data transmitter300 may be incorporated into transmitter 110 described in FIG. 1.

It is also important to note that several components andinterconnections necessary for complete operation of data transmitter500 are not shown in the interest of conciseness, as the components notshown are well known to those skilled in the art.

Data transmitter 500 comprises the following elements that are linkedtogether by a data and address bus 560:

-   -   a central processing unit (CPU) 510, which is, for example, a        microprocessor or a Digital Signal Processor (DSP);    -   a ROM 520 containing individual memory sections 522-526;    -   a RAM 530 containing individual memory section 532-538;    -   an interface 540 that receives data from an application or        source prior to transmission; and    -   a transmission module 550 that transmits the data as an output        signal on a wireless channel, the transmission module 550        including RF circuitry and antennas.

The functional aspects of elements 510, 520, and 530 are well known bythose skilled in the art and won't be disclosed further here. Thefunctional aspects of elements 540 and 550 are similar to thosedescribed above in either FIG. 1 or FIG. 3 and won't be describedfurther here.

In ROM 520 and RAM 530, the memory sections may correspond to an area ofsmall capacity (some bits) or to a very large area (e.g. a whole programor large amount of received or decoded data).

ROM 520 includes the following components:

-   -   a program section 522;    -   pre-encoder parameters section 524 (e.g., clipping parameters,        pre-filtering parameters and channel cancellation parameters);        and    -   STBC/SFBC parameters section 526 (e.g., STBC/SFBC code, number        of antennas).

Algorithm information, code, and/or software instructions related to theencoding and transmission method according to the present disclosure arestored in ROM 520. When switched on, the CPU 510 uploads the programfrom section 522 into RAM 530 and executes the correspondinginstructions.

RAM 530 comprises:

-   -   section 532 including memory space to hold the program executed        by the CPU 510 and uploaded after switching on data transmitter        500;    -   section 534 including memory space to hold input data;    -   section 536 including memory space to hold encoded data in        different during the encoding process; and    -   section 538 including memory space to hold other variables used        for encoding.

According to one embodiment, data transmitter 500 is implemented in apure hardware configuration in one or several floating point gate arrays(FPGA), application specific integrated circuit (ASIC) or very largescale integration (VLSI) circuits with corresponding memory. In anotherembodiment, data transmitter 500 is implemented using both VLSI circuitswith memory and DSP code.

Turning to FIG. 6, a block diagram of an exemplary pre-encoder 600according to aspects of the present disclosure is shown. Pre-encoderoperates in a manner similar to pre-encoder 320 in FIG. 3. Pre-encoder600 may further be used as part of a broadcast transmitter, such astransmitter 110 described in FIG. 1.

The pre-encoder 600 includes the following components:

-   -   an IFFT block 610 that receives a frequency domain multicarrier        modulated signal from a modulator circuit (e.g., modulator 310        in FIG. 3) and performs an inverse FFT on the signal;    -   a clipping block 620 coupled to the IFFT block 610 that clips        the level of the signal based on an additional signal labeled        Vclip applied to clipping block 620;    -   an FFT Block 630 coupled to the clipping block that performs an        FFT on the signal following clipping in the clipping block;    -   a subtractor 640 coupled to the FFT block 630 and also receiving        the frequency domain multicarrier modulated signal as a second        input, the subtractor 640 substracting the frequency domain        multicarrier modulated signal from the clipped signal to        generate a correction vector;    -   a multiplier 650 coupled to the subtractor 640 that amplifies        the correction vector by a gain value equal to K as an input to        multiplier 650 to generate a gain adjusted correction vector,        also referred to as an error vector;    -   an adder 660 coupled to the multiplier 650 and also receiving        the frequency domain multicarrier modulated signal as a second        input, the adder 660 adding the frequency domain multicarrier        modulated signal to the error vector to generate a projection        vector; and    -   a projection block 670 coupled to the adder 660 and also        receiving the frequency domain multicarrier modulated signal and        using the error vector from multiplier 650 as inputs, the        projection block 670 generates a new projected frequency domain        multicarrier modulated signal, also referred to as a reduced        PAPR frequency domain multicarrier modulated signal.

Pre-encoder 600 operates and processes the frequency domain multicarriermodulated signal as a series of symbols. One multicarrier symbol in thefrequency domain with complex QAM values of each subcarrier is processedin IFFT block 610 to obtain its time domain signal representation. TheIFFT block 610 may compute a representation that has been oversampledwith respect to the time domain in order to increase the performance orresolution of the further processing.

The time domain representation of the symbol is clipped in the clippingblock 620. Clipping is often referred to as limiting and involvespreventing the level, or value, of the signal or symbol from exceeding afixed value. The clipping block 620 uses a signal Vclip as an input forthe fixed value. In some embodiments, the signal Vclip may be constantand not adjustable, but in other embodiments, the signal Vclip may beadjustable and further dynamically adjustable. The clipping block 620may use a transfer function that includes a soft limiter function or,alternatively, a smooth compression function. Exemplary compressionfunctions may include, but is not limited to, hyperbolic tangent, A-Lawor μ-Law companding functions similar to those used in telephonesystems.

The clipped symbol from clipping block 620 is converted back from a timedomain representation of the symbol to a frequency domain representationof the symbol using FFT block 630, similar to the original input symbol.The multicarrier QAM modulated original multicarrier symbol is comparedto the clipped symbol using subtractor 640 to generate a correctionvector for the symbol. Although not shown, a buffer circuit may benecessary in order to synchronize the original multicarrier symbol withthe clipped symbol at the input of subtractor 640.

The correction vector for the symbol is multiplied by a fixed gain valueK in multiplier 650. The gain corrected vector for the symbol is addedback into the original symbol to generate a projection vector for thesymbol. It is important to note that the correction vector fromsubtractor 640 represents the extent to which the original symbol hasbeen clipped or limited as a value. This clipped region for the symbolis amplified to accentuate the clipping region in multiplier 650 andadded back with the original symbol in adder 660, resulting inexaggerated constellation projection for the symbol.

The resulting constellation projection for the symbol is furtherprocessed in projection block 670 using an allowed extendedconstellation mask in conjunction with the error vector for the symboland the original constellation projection for the symbol. Each point ofthe constellation may be associated to an extension mask. In oneembodiment, only the outer points of the constellation are associatedwith an extension mask. The extension mask represents a region in whicha constellation point may be projected without obscuring its originalsymbol location, and its symbol value, within the constellation. In someinstances, the extension mask may represent a line. In other instances,the extension mask may represent a region. Further details regardingconstellation point projections and extension masks will be describedbelow.

It is important to note that, for QAM constellations that are square,the real and imaginary components of the complex QAM values, or symbollocations, may be processed separately as scalar values. As a result, anextension mask associated with a square QAM constellation will representa line or series of lines in an x axis direction and/or a y axisdirection.

The output time domain OFDM signal is obtained using an OFDM modulator,such as modulator 114 in FIG. 1 or OFDM modulators 340 and 350 in FIG.3. The OFDM modulator uses the real and imaginary output signals,representing a reduced PAPR frequency domain signal, from projectionblock 670. It is important to note that, in some embodiments, the realand imaginary output signals may be combined to form a single vectorsignal.

Turning now to FIG. 7, a block diagram of another exemplary pre-encoder700 according to aspects of the present disclosure is shown. Pre-encoder700 is intended for use in a transmitter employing MIMO techniques orusing a plurality of modulation transmission circuits and antennas, suchas transmitter 300 described in FIG. 3. Specifically, pre-encoder 700operates in a manner similar to pre-encoder 320. Pre-encoder 700 will bedescribed based on a MIMO dimension equal to two, using two modulationcircuits.

The pre-encoder 700 includes the following components:

-   -   an STBC/SFBC encoder 710 that receives complex symbol data and        provides encoded complex symbols, the symbols typically arranged        in groups;    -   IFFT blocks 720 and 725 that perform an inverse FFT on the        encoded complex symbols;    -   clipping blocks 730 and 735 coupled to the IFFT blocks 720 and        725 respectively that clip the level of the signal based on an        additional signal or threshold level applied to clipping blocks        730 and 735;    -   FFT blocks 740 and 745 coupled to clipping blocks 730 and 735        respectively that perform an FFT on the signal following        clipping in clipping blocks 730 and 735;    -   an STBC/SFBC decoder 750 coupled to both FFT block 740 and FFT        block 745 that receives the complex FFT symbols and decodes the        symbols to produce complex symbol data to be processed;    -   a subtractor 760 that subtracts the originally provided complex        symbol data from the output of the STBC/SFBC decoder 750;    -   a multiplier 770 that multiplies the result of the subtraction        in subtractor 760 by a predetermined gain value equal to K;    -   an adder 780 that adds the result of the multiplication made by        multiplier 770 to the originally provided complex symbol data;        and    -   a projection block 790 that processes the result of the addition        made by the adder 780 to produce a projection onto a        constellation and provides the result of the projection for        further processing.

In operation, an input signal that has been modulated or processed usingdigital modulation (e.g., QAM modulation) and mapped into a series ofsymbols, is provided to STBC/SFBC encoder 710. The symbols may begrouped and encoded by STBC/SFBC encoder 710 to form a STBC/SFBCcodeword in a manner similar to that described earlier in FIG. 3. Theindividual groups of codewords are provided to IFFT blocks 720 and 725.The time domain signal is first obtained in IFFT blocks 720 and 725. TheIFFT blocks 720 and 725 may compute an oversampled version of the timedomain signal to increase the performances (especially to improve peaklocalization after IFFT processing and avoid peak regrowth indigital/analog conversion). According to a variant of the presentdisclosure, no oversampled version of the time domain signal iscomputed.

Time domain signals from IFFT blocks 720 and 725 is clipped, orcompressed in amplitude, in clipping blocks 730 and 735 based on athreshold. In one embodiment, clipping blocks 730 and 735 may use afixed threshold. In other embodiments, the threshold may be adjustableand further dynamically adjustable. Further processing in FFT blocks 740and 745 returns the signal to the frequency domain. The FFT blocks 740and 745 operate in a manner to reverse the processing of IFFT blocks 720and 725, including any signal resampling as necessary. STBC/SFBCdecoding is applied to the frequency domain clipped signals from each ofthe FFT blocks 740 and 745 in the STBC/SFBC decoder 750. The decoding inSTBC/SFBC decoder is intended to reverse the processing performed inSTBC/SFBC encoder 710.

Except as described below, the operation of the remaining blocks inpre-encoder 700 operate in a manner similar to subtractor 640,multiplier 650, adder 660, and projection block 670 described in FIG. 6and will not be described in further detail here.

In some embodiments using either pre-encoder 600 or pre-encoder 700,some parts of the signal may not be modified using the pre-encodingprocessing techniques. These parts may include, but are not limited to,reference or pilot signals, such as scattered or continuous pilotsignals used for channel estimation. For these parts of the signal, thecorrection signal may be set to zero. The operation may be carried outas part of the subtractor (e.g., subtractor 640 or subtractor 760). Theoperation may also be carried out as part of the multiplier (e.g.,multiplier 650 or multiplier 770) by setting the gain value K equal tozero for these parts of the signal. The operation may further be carriedout in the projection block (e.g., projection block 670 or projectionblock 790) by preventing a projection change in position for thesymbol(s).

In some embodiments, variable and different values for gain value may beapplied as separate values Ki to each individual carrier, symbol, orportion of the signal. The values for Ki may be determined based on thetransmitted values. Alternatively, the values for Ki may be obtainedthrough a digital optimization algorithm. Ki values may be dependent onthe number or carriers, the modulation, the definition of the extendedconstellation, the PAPR target, and/or the possible increase of powertransmission. Different values for Ki may be generated based on thenumber of carriers in order to balance the distortions of power of thespectrum as a result of clipping. For example, a signal using 1705modulated carriers using 64 QAM constellation extended to constellationextension value of 81 to achieve the desired value of PAPR, a Ki valuefor all portions of the signal equal to 15 may be used. Advantageously,Ki values in the range between 10 and 25 may be used depending on theallowed power increase and desired PAPR.

In one embodiment using pre-encoder 600 or pre-encoder 700, a non nullvalue for Ki is applied to all symbols associated with modulatedcarriers. Any symbols associated with carriers that are non-modulatedcarriers (i.e., carriers not used to transmit data) are reset to zeroafter the pre-encoding process. According to a variant, all or some ofsymbols associated with non-modulated carriers are multiplied by a nonnull value for Ki in the multiplier (e.g., multiplier 650 or multiplier770) and left unmodified by the projection block (e.g., projection block670 or projection block 790).

As described earlier, previous PAPR techniques using a pre-encodersimilar to that described here in FIG. 6 or FIG. 7 have been configuredfor processing symbols that use a square constellation, such as a 16-QAMsquare constellation. FIG. 8 shows a diagram 800 for a 16-QAM squareconstellation. The constellation is projected with symbol pointsoriented along a real axis 810 and an imaginary axis 820.

Only the boundary points of the constellation, points 830-841, are shownextended using the PAPR techniques such as those described forpre-encoder 600 in FIG. 6 and pre-encoder 700 in FIG. 7. Further, thefour corner points, points 830, 833, 836, and 839 may be extended toanywhere within the hatched areas 860-863 respectively. It is importantto note that hatched areas 860-863 are square or rectangular in natureand may be projected using simple scalar values in either real orimaginary axis projection. The other boundary points, 831-832, 834-835,837-838, and 840-841 may only be extended following the line segments870-877, starting at the point and extending along the real or imaginarydirection toward the outside of the constellation. If any otherprojection for these boundary points occurs, a potential decoding errormay result due to improper symbol decoding. The projection extensionregion is also limited by an upper bound. The upper may be determined ordefined by parameters associated with the signal transmission equipment(e.g., performance specifications for circuitry in antenna 125 describedin FIG. 1 or circuit in antennas 360 and 370 described in FIG. 3). Theprojection extension, as shown here in FIG. 7, as well as the extensionsshown below, may also be referred to as a discrete constellationextension.

The four inner points, 850-853, are shown as unaffected or notre-projected by the PAPR techniques.

The technique applied in FIG. 8 and implemented in diagram 800 as partof a pre-encoder 600 or pre-encoder 700 is commonly called “ActiveConstellation Extension” (ACE) and has been used in the DVB-T2 standardEN 302 755. The technique is used with QAM modulated carriers usingsquare constellation patterns because the boundary points of the squareQAM constellation are extended following the real or imaginary axisdirection.

The constellation extension and projection techniques using scalarprojections, such as shown in diagram 800, are less efficient when usedwith non-square constellations. FIG. 9 shows a diagram 900 for a 16-QAMnon-square constellation with the constellation extension and projectiontechniques applied in a manner similar to diagram 800. The constellationis projected with symbol points oriented along a real axis 910 and animaginary axis 920.

Diagram 900 includes outer constellation points 930-937 and inner points940-947. As in diagram 800, points 940-947 shown in diagram 900 are notaffected by the constellation extension projection techniques. Diagram900 includes an extension projection mask shown as dashed lines. Theextension region is limited to only 8 lines, shown as 970-977 for thistype of constellation. Due to relative position of constellation points930-937, the extension regions are reduced compared to regions or maskfor a square 16-QAM constellation. Any change in the extension regionsshown in diagram 900 is not possible without creating unnecessary symbolerrors.

The issues with scalar constellation extension and projection techniquesare further accentuated with higher order constellations. FIG. 10 showsa diagram 1000 for a 64-QAM non-square constellation with theconstellation extension projection techniques applied in a mannersimilar to diagram 800. The constellation is projected with symbolpoints oriented along a real axis 1010 and an imaginary axis 1020.

Diagram 1000 includes outer constellation points 1030-1045. As indiagram 900, the remaining inner points, shown here not labeled, are notaffected by the constellation extension projection techniques. Diagram1000 includes extension projection mask shown as dashed lines 1070-1085.The extended region is limited to only 16 lines for this constellation.Due to relative position of constellation points 1030-1045, theextension regions are reduced compared to a square 64-QAM constellationand cannot be expanded without creating unnecessary symbol errors.

Constellation projection and extension techniques may be improved inorder to provide a more optimal extension mask for non-squareconstellations, such as shown in FIG. 9 and FIG. 10. Instead ofextending the real and imaginary components in different processes, asdescribed in FIG. 6 and FIG. 7, the projection is done using both realand imaginary components in a projection block (e.g., projection block670 or projection block 790) simultaneously or together and combined.The projection block is modified to use a vector error signal as opposedto a scalar (i.e., real and imaginary) error signal in order to work intwo dimensions simultaneously in extending the positions of the complexconstellation values. The modification allows the extension mask to bedefined in two dimensions, or as a vector, in order to increase theextended regions of each boundary point of the constellation. As aresult, the extension follows the vector direction of the extendableconstellation points. The extended region is a set of angular sectorswith the vertex at the constellation point and an angle equal to theprojection angle between two adjacent symbols and origin point for theconstellation. For most non-square or constellations, the boundary linesfor the angular sectors will be non-orthogonal.

Turning to FIG. 11, a diagram 1100 illustrating the constellationextension techniques on a 64-QAM non-square constellation according toprinciples of the present disclosure is shown. Diagram 1100 illustratesthe projection and projection extension mask using several projectionscenarios and techniques based on using elements described above in FIG.6 and FIG. 7. The constellation is projected with symbol points orientedalong a real axis 1110 and an imaginary axis 1120.

Diagram 1100 includes outer constellation points 1130-1145. As indiagram 1000, the remaining inner points, shown here not labeled, arenot affected by the constellation extension projection techniques. A setof first projection lines, labeled 1150-1165, are shown projecting fromthe origin (i.e., intersection of axis 1110 and axis 1120) to each outerconstellation point 1130-1145 respectively. An angle θ represents theangular distance between any two outer constellation points of theconstellation. The angle θ also represents an angular sector region inwhich an extension of any outer constellation may exist withoutproducing an increase in symbol error probability for the symbol. Theangular sector is shown as a region defined by dashed lines 1170 a-1170b through 1185 a-1185 b. The extended region of the boundaryconstellation point is defined by the opening angle of the angularsector with the vertex at the original position for the point of theconstellation.

The extension projection mask, as shown in diagram 1100, may be producedby processing the error signal from the multiplier (e.g., multiplier 650or multiplier 770) along with the corrected signal from the adder (e.g.,adder 660 or adder 780). By processing the error signal as a vectorsignal, an angular region may be produced for the extension region forthe location of the outer constellation points in the constellation. Theangular region is further determined in the projection block (e.g.,projection block 670 or projection block 790) based on the constellationthat is being used. It should be pointed out that the angular sector forthe extension region is determined by the angular distance (e.g., angleθ in diagram 1100) between any two adjacent outer constellation points(e.g., points 1130-1145). The angular distance, and therefore, theangular sector for the extension region, may be different for differentconstellations.

It is important to note that the angular distance between the twoadjacent outer constellation points, or angle θ, represents the maximumangular sector for the extension mask. An angular sector smaller thanthe maximum angular sector may also be used with reduced efficiency.

Turning to FIG. 12, a diagram 1200 illustrating the application of theextension mask to one point of the constellation with respect todifferent cases of the input signal of the projection block according toaspects of the present disclosure is shown. Diagram 1200 illustrates theprojection and projection extension mask using several projectionscenarios based on the projection techniques described above in FIG. 11using elements such as those described above in FIG. 6 and FIG. 7. Asingle constellation point and accompanying region is shown orientedalong an x-axis 1210 and a y-axis 1220 with an origin point 1225.

The initial symbol location in the constellation at the input of thepre-encoder is shown as point labeled 1230. The extension maskassociated to the point 1230 is limited by the two lines 1240 and 1245.The open angle between 1240 and 1245 is an input parameter of theprojection block. The maximum open angle is fixed for each type ofconstellation. However, an open equal to or less than the maximum openangle may be used. For example, the angular sector bound by lines 1240and 1245 may be based on the angular distance between point 1230 and anadjacent symbol point, not shown. The angle bisector for the lines 1240and 1245 is line 1250, shown as a dash-dot line, and passes through thecenter of the constellation, point 1225, and through point 1230.

The processing performed in a pre-encoder (e.g., pre-encoder 600 orpre-encoder 700) related to clipping, subtracting, and multiplying thesignal may alter the position of the constellation symbol (e.g., point1230). The projection block (e.g., projection block 670 or projectionblock 790) will re-position the symbol based on the techniques of thepresent disclosure. The following projection scenarios illustrated bypoints in diagram 1200 are further described here.

In a first scenario, the point labeled 1260 is considered. Point 1260 isinside the radial arc 1235 that is formed from the center 1225 andpassing through 1230. As a result, point 1260 is projected to theoriginal point 1230 because it cannot be projected in the extensionmask.

In a second scenario, the point labeled 1265 is considered. Point 1265is on the arc 1235. As a result, the point 1265 is also projected to theoriginal point 1230 because it cannot be projected in the extensionmask.

In a third scenario the points labeled 1280 and 1285 are considered.Points 1280 and 1285 are both outside the arc 1235 and will need to beprojected in the extension mask. The point 1280 is outside the extensionmask but it is projected onto an arc 1270 which has a center 1225 andpasses through point 1280 as a well as a point 1282. Point 1282 is onthe line 1240 representing the edge of the angular sector representingthe extension mask for point 1230. As a result, point 1280 is projectedto point 1282 in order to reposition the original point 1280 within theextension mask for point 1230. Similarly, the point 1285 is projectedfollowing arc 1270 and passing through 1285 as well as point 1287. Point1287 is on the line 1245 representing the edge of the angular sectorrepresenting the extension mask for point 1230. As a result, point 1285is projected to point 1287 in order to reposition the original point1285 within the extension mask for point 1230.

In a fourth scenario, the point labeled 1290 is considered. Point 1290is located inside the extension mask for point 1230 and defined byextension lines 1240 and 1245. As a result, the location for point 1290is not changed or re-projected.

Turning to FIGS. 13-15, a set of graphs 1300-1500 illustrating thesimulated performance comparison for PAPR reduction techniques accordingto the principles of the present disclosure is shown. Each of thesimulated performance results were generated using a signal operating ina DVB-T2 operating in 32K FFT mode in a 6 MHz wide channel. Theoperating condition represents a worst case condition. The signal doesnot contain either continuous or scattered pilot carriers.

The simulations are based on an implementation using a pre-encodersimilar to pre-encoder 600 described in FIG. 6. Specifically, the valuefor V_(clip) used in clipping block 620 is adjustable within the range[1.0; 3.5]. Further the value for K used in multiplier 650 is adjustablewithin the range [1; 63]. For each simulation shown in FIGS. 13-15, thevalues for V_(clip) and K are optimized to get the best PAPR reduction.

Graph 1300 shows the PAPR in (dB) along the x-axis, labeled 1310, inrelation to the Complementary Cumulative Distribution Function (CCDF) asthe probability that (power>PAPR) along the y-axis, labeled 1320. TheCCDF represents the distribution of probability of PAPR according to thePAPR for each sample or symbol of the signal. Graph 1300 shows resultsfor a 16 point non-square constellation, such as shown in FIG. 9. Graphline 1330 represents the results with no PAPR reduction applied to thesignal. Graph line 1340 represents the results using the DVB-T2 ACEtechniques similar to those described in FIG. 8. Graph line 1350represents the results using the improved techniques of the presentdisclosure, referred to as 2-D ACE techniques, similar to thosedescribed in FIG. 11.

Graph 1400 shows the PAPR in (dB) along the x-axis, labeled 1410, inrelation to the CCDF as the probability (power>PAPR) along the y-axis,labeled 1420. Graph 1400 shows results for a 64 point non-squareconstellation, such as shown in FIG. 10. Graph line 1430 represents theresults with no PAPR reduction applied to the signal. Graph line 1440represents the results using the DVB-T2 ACE techniques. Graph line 1450represents the results using the improved techniques of the presentdisclosure.

Graph 1500 shows the PAPR in (dB) along the x-axis, labeled 1510, inrelation to the CCDF as the probability (power>PAPR) along the y-axis,labeled 1520. Graph 1500 shows results for a 256 point non-squareconstellation. Graph line 1530 represents the results with no PAPRreduction applied to the signal. Graph line 1540 represents the resultsusing the DVB-T2 ACE techniques. Graph line 1550 represents the resultsusing the improved techniques of the present disclosure.

The results for the graphs in FIGS. 13-15 are summarized in Table 1.

TABLE 1 Improvement PAPR using 2-D ACE reduction technique ConstellationAlgorithm Vclip K (dB) (dB) 16 point non- DVB-T2 2 25 4.1 square ACE 2-DACE 1.9 19 4.3 0.2 64 point non- DVB-T2 2.2 63 3.2 square ACE 2-D ACE 236 4.1 0.9 256 point DVB-T2 2.4 63 1.5 non-square ACE 2-D ACE 2.2 61 3.11.6

Turning now to FIG. 16, a flow chart of an exemplary process 1600 forreducing the PAPR in a signal according to aspects of the presentdisclosure is shown. Process 1600 describes a mechanism for reducingPAPR in a signal that includes or uses non-square constellation patternsfor signal transmission. Process 1600 will primarily be described interms of the pre-encoder 600 described in FIG. 6. Process 1600 may beequally applied to the operation of pre-encoder 700 described in FIG. 7.Process 1600 may also be used in transmitter 110 as part system 100described in FIG. 1 or as part of data transmitter 300 described in FIG.3. It is also important to note that some steps in process 1600 may beremoved or reordered in order to accommodate specific embodimentsassociated with the principles of the present disclosure.

At step 1605 a signal is received. The signal may contain audio, video,signaling or control and other ancillary data (e.g., program guidedata). The signal may be processed and may be a frequency domainrepresentation of the signal content. Next, at step 1610, the signal ismapped to one or more symbols in a multiple transmission signalingarrangement. The mapping, at step 1610, may be performed in a STBC/SFBCencoder (e.g., STBC/SFBC encoder 710 described in FIG. 7.) The mapping,at step 1610, may involve generating a plurality of portions of theoriginal signal using one or more known codeword sets including, but notlimited to, a Golden code. The mapping, at step 1610, is particularlysuited for use in MIMO transmission.

At step 1615, the mapped signal generated at step 1610 is converted to atime domain signal. In some embodiments, the time domain conversion, atstep 1615, may return the signal received, at step 1605, to a signaloriginally provided by a content source (e.g., content source 111described in FIG. 1). The conversion, at step 1615, may be performedusing an IFFT block (e.g., IFFT block 610) or any similar transformprocessing block.

Next, at step 1620, the amplitude level of the time domainrepresentation of the signal generated at step 1615 is limited,compressed, or clipped in order to reduce the signal amplitude level.The limiting, compressing, or clipping, at step 1620, may be performedin a clipping circuit (e.g., clipping block 620) or any similar circuit.In one embodiment, the signal generated at step 1615 is clipped based onan additional signal, Vclip. In other embodiments, the signal generatedat step 1615 may be clipped, limited, or compressed using transferfunction that includes a soft limiter function or, alternatively, asmooth compression function.

At step 1625, the amplitude limited signal is converted back to afrequency domain representation of the signal. The conversion, at step1625, may be performed using an FFT block (e.g., FFT block 630) or anysimilar transform processing block. In some embodiments, the conversion,at step 1625 is an exact inverse of the conversion, at step 1615.

At step 1630, the frequency domain representation of the signal ismapped back from a set of symbols suitable for a plurality of signals ina multiple transmission signaling arrangement to a single signal. Themapping, at step 1630, may be performed in a STBC/SFBC decoder (e.g.,STBC/SFBC decoder 750 described in FIG. 7.) The mapping, at step 1630,may involve demapping or decoding the plurality of portions of theoriginal signal using one or more known codeword sets including, but notlimited to, a Golden code. The mapping, at step 1630, is particularlysuited for use in MIMO transmission.

At step 1635, the new signal generated, at step 1630, in the frequencydomain is subtracted from the original signal received, at step 1605.The step of subtraction, at step 1635, may also include buffering theoriginal signal in order to synchronize or time align the originalsignal with the new signal. Next, at step 1640, the resulting signal,from step 1635, is multiplied by a constant. Constant value may be asignal value K for all signals and symbols. In other embodiments,variable and different values for gain value may be applied as separatevalues Ki to each individual carrier, symbol, or portion of the signal.The values for Ki may be determined based on the transmitted values.Alternatively, the values for Ki may be obtained through a digitaloptimization algorithm. Ki values may be dependent on the number orcarriers, the modulation, the definition of the extended constellation,the PAPR target, and/or the possible increase of power transmission.Different values for Ki may be generated based on the number of carriersin order to balance the distortions of power of the spectrum as a resultof either unintentional clipping or intentional amplitude limiting, atstep 1620.

At step 1645, the multiplied or amplified signal, from step 1640, isadded to the original signal received, at step 1605. The step ofaddition, at step 1645, may also include buffering the original signalin order to synchronize or time align the original signal with themultiplied or amplified signal. Next, at step 1650, the resultingsignal, from step 1645, is projected into a constellation projectionextension mask. The constellation projection mask is based on theoriginal constellation, using the received signal (e.g., the signalreceived at step 1605). The projection, at step 1650, may be carried outin a projection circuit or projection block (e.g., projection block 670described in FIG. 6 or projection block 790 described in FIG. 7). Apoint or symbol that is projected, at step 1650, may be associated to anextension mask. In one embodiment, only the outer points of theconstellation for the signal are associated with an extension mask. Theextension mask represents a region in which a constellation point may beprojected without obscuring its original symbol location, and its symbolvalue, within the constellation. In some instances, the extension maskmay represent a line. In other instances, the extension mask mayrepresent a region.

In a preferred embodiment, the projection, at step 1650, may be producedby processing the signal from the multiplication, at step 1640, alongwith the signal from the addition, at step 1645. By processing thesignals as vector signals, an angular region may be produced for theextension region for the location of the outer constellation points inthe constellation. The angular region may be further determined based onthe constellation that is being used. It should be pointed out that amaximum angular sector for the extension region may be determined by theangular distance (e.g., angle θ in diagram 1100) between any twoadjacent outer constellation points (e.g., points 1130-1145). Theangular distance, and therefore, the maximum angular sector for theextension region, may be different for different constellations.Further, an angular sector that is less than the maximum angular sectormay also be used.

At step 1655, the projected signal, representing a stream of reducedPAPR OFDM symbols, is modulated using an IFFT, to produce a time domainreduced PAPR OFDM signal. The modulation, at step 1655 may be performedin a modulator (e.g., modulator 114 described in FIG. 1 or OFDMmodulators 340 and 350 described in FIG. 3). In some embodiments, themodulating, at step 1655, may further include mapping of the signal intoa set of symbols for use in a multiple signal transmission environmentemploying MIMO techniques.

At step 1660, the time domain reduced PAPR OFDM signal is transmitted.The transmission, at step 1660, may be carried out by transmissioncircuits and may use one or more antennas for wireless transmission orbroadcast (e.g., antenna 115 described in FIG. 1 or antennas 360 and 370described in FIG. 3).

One or more of the steps of process 1600 may be rearranged, combined, oromitted. For example, in embodiments utilizing a SISO transmissionconfiguration, including broadcast signal embodiments (e.g., ATSC 3.0 orDVB-T2), steps 1610 and 1630 may be omitted. Further, the generation ofthe projection constellation extension, at step 1650, may be producedthrough a series of process steps that differ from steps 1610 to 1645.As such, these different steps still encompass a process forpre-encoding the signal in order to permit the projection, at step 1650,of the processed signal onto a constellation projection extension asdescribed herein.

In an embodiment using at least some of the steps of process 1600, asignal may be received that has been encoded using a specific FECencoding structure that encodes the data in the signal at one or moredifferent code rates. Several types of encoding structures are possible,including those described earlier in conjunction with DVB-T2 and ATSC3.0 or others well known in the art. As a result, the constellationprojection mask may depend on the code rate for the data as well as theconstellation used for the transmission of the signal. Further, theangular distance (e.g., angle θ) for the outer constellation points inconstellation may depend on both the constellation and the code rate.Table 2 shows an exemplary set of values for the angle θ given differentconstellations and code rates used as part of the ATSC 3.0 system:

TABLE 2 Code Rate 2/ 3/ 4/ 5/ 6/ 7/ 8/ 9/ 10/ 11/ 12/ 13/ Constellation15 15 15 15 15 15 15 15 15 15 15 15 16QAM NA 33.26° 35.6° 38.5° 44.14°44.1° 44.49° 44.49° 42.1° NA NA NA 64QAM 22.96° 39.36° 41.26° 19.01°21.17° 22.49° 22.28° 22.49° 22.4° 19.75° 18.42° 16.81° 256QAM 36.67°40.26° 19.11° 22.47° 8.38° 11.23° 11.23° 10.93° 11.22° 10.63° 8.8° 8.34°

According to specific embodiments of the disclosure, set of values forthe angle θ is fully or partially defined by Table 2. According tospecific embodiments of the disclosure, values for the angle θ aredifferent. According to a variant of the disclosure, other codes ratesor constellations are used and values for the angle θ are definedaccordingly.

It is important to note the values given in Table 2 can be consideredspecific to the ATSC 3.0 system. However, other systems, using differentconstellations, different code rates, and possibly even differentformats may use a different set of values for angle θ in order toachieve similar results based on the principles of the presentdisclosure.

A system may employ signals that use a non-square constellation for somesignal formats while using other constellation types for other signalformats. In one embodiment using at least of the steps of process 1600,a signal may use a non-square constellation, referred to as a twodimensional (2D) constellation for some signal formats while using asquare constellation, referred to as a one dimensional (1D)constellation for other signal formats. Table 3 shows a specificimplementation for type of constellation (1D or 2D) for differentconstellation sizes as well as difference code rates used as part of theATSC 3.0 system:

TABLE 3 Code Rate 2/ 3/ 4/ 5/ 6/ 7/ 8/ 9/ 10/ 11/ 12/ 13/ Constellation15 15 15 15 15 15 15 15 15 15 15 15 QPSK 1D 1D 1D 1D 1D 1D 1D 1D 1D 1D1D 1D 16QAM 1D 2D 2D 2D 2D 2D 2D 2D 2D 1D 1D 1D 64QAM 2D 2D 2D 2D 2D 2D2D 2D 2D 2D 2D 2D 256QAM 2D 2D 2D 2D 2D 2D 2D 2D 2D 2D 2D 2D 1024QAM 1D1D 1D 1D 1D 1D 1D 1D 1D 1D 1D 1D 4096QAM 1D 1D 1D 1D 1D 1D 1D 1D 1D 1D1D 1D

According to specific embodiments of the disclosure, types ofconstellations are fully or partially defined by Table 3. According tospecific embodiments of the disclosure, types of constellations aredifferent (e.g. a non square constellation may be used for 1024 QAM or4096 QAM). According to a variant of the disclosure, other codes ratesor constellations are used.

Signals using 2D constellations may employ a PAPR process, such asdescribed by process 1600. Signals using 1D constellation may employ aPAPR process similar to that shown and described in FIG. 8 and FIG. 9.Collectively, the processing of 1D and 2D constellations to reduce PAPRmay be referred to as active constellation extension (ACE) techniques.Further, ACE techniques, such as the PAPR process described in FIG. 16,or other PAPR processes for 1D constellation, when used in conjunctionwith OFDM, are typically applied only to the portion of the signal thatincludes data and typically not be applied to pilot carriers or reservedtones included as part of the signal. In systems, such as the ATSC 3.0system, ACE techniques are applied only to the portion of the signalthat includes data and is not applied to pilot carriers or reservedtones included as part of the signal. Another PAPR process, called ToneReservation (TR) introduces reserved tones into the OFDM symbols toreduce PAPR. In ATSC 3.0, if both ACE and TR are used, the ACE isapplied to the signal first.

Further, the PAPR techniques may not be used in conjunction with the useof level division multiplexing (LDM) or when either MIMO or MISOoperational modes are used in a system. In system, such as the ATSC 3.0system, PAPR techniques, and specifically ACE, is not used inconjunction with the use of level division multiplexing (LDM) or wheneither MIMO or MISO operational modes. Finally, the use, or lackthereof, of the active constellation techniques may be indicated in thesignal as part of a header or other informational layer such as, but notlimited to, the L1 signaling in DVB-T2 or ATSC 3.0.

Turning now to FIG. 17, a block diagram of a further exemplarypre-encoder 1700 according to aspects of the present disclosure isshown. Pre-encoder 1700 operates in a manner similar to pre-encoder 600described in FIG. 6. Pre-encoder also operates in a manner similar topre-encoder 320 in FIG. 3. Pre-encoder 1700 may further be used as partof a broadcast transmitter, such as transmitter 110 described in FIG. 1.Except as described below, elements 1710, 1720, 1730, 1740, 1750, 1760,and 1770 are similar in function to elements 610, 620, 630, 640, 650,660, and 670 described in FIG. 6 and will not be further described here.

In pre-encoder 1700, a signal, labeled x′=[x′₀, x′₁, . . . , x′_(N)_(FFT) ₋₁] is obtained from an input signal x through interpolation by afactor of 4 in interpolator 1712 followed by low-pass filter 1715. Thecombination of IFFT 1710, oversampling through interpolator 1712, andlow-pass filtering in low-pass filter 1715 is implemented using zeropadding and a four times oversized IFFT operator as part of IFFT 1710.

A signal labelled x″=[x″₀, x″₁, . . . , x″_(N) _(NFFT) ₋₁] is obtainedby applying a clipping operator in clipping block 1720 to the signallabeled x′. The clipping operator in clipping block 1720 is defined asfollows:

$\begin{matrix}{x_{k}^{''} = \left\{ \begin{matrix}{x_{k}^{\prime},} & {{{if}\mspace{14mu} {x_{k}^{\prime}}} \leq V_{clip}} \\{{V_{clip} \cdot \frac{x_{k}^{\prime}}{x_{k}^{\prime}}},} & {{{if}\mspace{14mu} {x_{k}^{\prime}}} > V_{clip}}\end{matrix} \right.} & \left( {{equation}\mspace{14mu} 2} \right)\end{matrix}$

The clipping threshold V_(clip) is a parameter of the activeconstellation extension algorithm and techniques. For example, theclipping threshold V_(clip) may be selectable in the range between +0 dBand +12.7 dB in 0.1 dB steps above the standard deviation of theoriginal time-domain signal.

A signal labeled x_(c)=[x_(c0), x_(c1), . . . , x_(cN) _(FFT) ₋₁] isobtained from the signal labelled x″ through lowpass filtering inlow-pass filter 1722 and decimation by a factor of 4 in decimator 1725.A signal labeled X_(c) is obtained from x_(c) using an FFT operation inFFT block 1730. The combination of low-pass filtering in low-pass filter1722, downsampling in decimator 1725, and FFT operations in FFT block1730 is implemented using a four times oversized FFT operator.

The Error vector, labeled E, is obtained by combining, through asubtraction and gain multiplication operation, the signals labeled X_(c)and X in subtractor 1740 and gain block 1750 as follows:

E=G·(X _(c) −X)   (equation 3)

The extension gain G is a parameter of the active constellationextension algorithm and techniques. For example, the value for theextension gain G may be selectable in the range between 0 and 31 insteps of 1.

The Extension vector, labeled V_(ext), is obtained or generated as anoutput from projection block 1770 as follows:

$\begin{matrix}{\mspace{79mu} {{\arg\left( V_{{ext},k} \right)} = \left\{ {\begin{matrix}{\frac{\theta}{2},} & {{{{{if}\mspace{14mu} \frac{\theta}{2}} < \phi_{e,k} < {90{^\circ}}};}\;} \\{{- \frac{\theta}{2}},} & {{{{if}\mspace{14mu} - {90{^\circ}}} < \phi_{e,k} < {- \frac{\theta}{2}}};} \\{\phi_{e,k},} & {else}\end{matrix}.} \right.}} & \left( {{equation}\mspace{14mu} 4} \right) \\{{V_{{ext},k}} = \left\{ \begin{matrix}{{E_{k}},} & {{if}\mspace{14mu} \left( {{E_{k}} \leq {L - {X_{k}}}}\; \right)\mspace{11mu} {AND}\mspace{14mu} \left( {\frac{\theta}{2} < \phi_{e,k} < {90{^\circ}}} \right)} \\{{L - {X_{k}}},} & {{{if}\mspace{14mu} \left( {{E_{k}} > {L - {X_{k}}}}\; \right)\mspace{14mu} {AND}\mspace{14mu} \left( {{{- 90}{^\circ}} < \phi_{e,k} < {- \frac{\theta}{2}}} \right)}\mspace{11mu}} \\{0,} & {else}\end{matrix} \right.} & \left( {{equation}\mspace{14mu} 5} \right)\end{matrix}$

The element φ_(e) denotes the angle between the argument of referencesymbol X and the Error vector E. A limiting element, labeled maximalextension value L may be applied and is a parameter of the activeconstellation extension algorithm and techniques. For example, themaximal extension value L may be selectable in the range between 1.8 and2.4 in 0.1 steps.

The angle θ is also an input parameter to the active constellationextension algorithm and techniques in pre-encoder 1700 and is dependenton the constellation dimension (e.g., for each 2D constellationdescribed earlier) as well as the forward error correction code rate. Anexemplary set of values for angle θ for a set of constellations and coderates are described earlier in Table 2.

A signal labeled X_(ACE) is generated or constructed by adding theExtension vector, labeled V_(ext), to the signal, labeled X, in adder1760 and as a selection in extension switch 1775, as follows:

$\begin{matrix}{X_{{ACE},k} = \left\{ {\begin{matrix}{{X_{k} + V_{{ext},k}},} & {{{if}\mspace{14mu} X_{k}\mspace{14mu} {is}\mspace{14mu} {extendable}};} \\{X_{k},} & {else}\end{matrix}.} \right.} & \left( {{equation}\mspace{14mu} 6} \right)\end{matrix}$

A component of the signal, labeled X_(k), is defined as extendable if itis an active cell (i.e. an OFDM cell carrying a constellation point),and if it carries a boundary point of the modulation constellation usedfor that cell. A component X_(k) may also defined as extendable if it isa dummy cell, a bias balancing cell, or an unmodulated cell in the FrameClosing Symbol, as defined and used in modulation systems, such asDVB-T2 and ATSC 3.0. For example, a component belonging to a 256-QAM9/15 modulated cell in an ATSC 3.0 format signal is a boundary point ofthe constellation if its modulus is greater than or equal to 1.65.

A signal labeled X_(ACE) is obtained or generated from X_(ACE) throughan IFFT operation in IFFT block 1780 and represents the output signalfor pre-encoder 1700.

FIGS. 18A and 18B show a series of diagrams for a 16-QAM non-squareconstellation having different error correction code rates applying PAPRtechniques according to aspects of the present disclosure. Inparticular, FIGS. 18A and 18B show the different angles θ that may beused in a pre-encoder (e.g., pre-encoder 1700 described in FIG. 17) forsignals using different FEC code rates. The code rates and angles θ thatare shown in FIGS. 18A and 18B are similar to the code rates and anglesincluded for a 16-QAM 2D constellation described earlier in Table 2.

FIGS. 19A and 19B show a series of diagrams for a 64-QAM non-squareconstellation having different error correction code rates applying PAPRtechniques according to aspects of the present disclosure. Inparticular, FIGS. 19A and 19B show the different angles θ that may usedin a pre-encoder (e.g., pre-encoder 1700 described in FIG. 17) forsignals using different FEC code rates. The code rates and angles θ thatare shown in FIGS. 19A and 19B are similar to the code rates and anglesincluded for a 64-QAM 2D constellation described earlier in Table 2.

FIG. 20 shows a series of diagrams for a 256-QAM non-squareconstellation having different error correction code rates applying PAPRtechniques according to aspects of the present disclosure. Inparticular, FIG. 20 shows the different angles θ that may be used in apre-encoder (e.g., pre-encoder 1700 described in FIG. 17) for signalsusing different FEC code rates. The code rates and angles θ that areshown in FIG. 20 are similar to the code rates and angles included for a256-QAM 2D constellation described earlier in Table 2.

A signal may be transmitted using the principles of the presentdisclosure. The signal may consist of a time domain representation ofsymbols in a constellation. The signal may include symbols mapped to aplurality of constellations. One or more of the constellations may benon-square constellations including, but not limited, to a 16 QAMnon-square constellation, and 64 QAM non-square constellation, and a 256QAM non-square constellation. One or more of the symbol locations may beadjusted based on a projection, such as the constellation projectionextensions described above. In one embodiment, one or more symbols areprojected into a constellation projection extension region that isrepresented by an outward angular sector based on the original orcorrect symbol location(s). The outward angular sector is formed usingthe projection angle formed between the original or correct symbollocation(s) and adjacent symbol locations. The projection angle forms afirst boundary and a second boundary for the outward angular region, thevalue for the projection angle being based on the constellation patternfor the signal as well as a code rate for the stream of data. In oneembodiment, the transmitted signal is an OFDM signal. In anotherembodiment, the transmitted signal complies with a transmission, such asDVB-T2 or ATSC3.0.

The signal transmitted using the principles of the present disclosurehas a reduced PAPR. The reduced PAPR signal may offer several advantagesincluding improving the efficiency of the HPA and minimizing distortionthat create undesired noise within the signal as well as in frequencyranges adjacent to the frequency range for the transmitted signal.

It is important to note that the techniques of the present disclosurealso applies to non uniform, non square constellations similar to thoseshown FIGS. 18A, 18B, 19A, 19B and 20. Non uniform constellations mayprovide better performance with simulations showing an improvement 1.5dB compared to the use of uniform constellations. According to avariant, the techniques may also be applied to other uniform, non squareconstellations such as Amplitude Phase Shift Keying (APSK)constellations.

The transmitted signal using the mechanisms of the present disclosuremay be received and decoded using a receiver device adapted to receivethe transmitted signal. For example, the transmitted signal may bereceived by a broadcast receiver (e.g., receiver 120 described in FIG.1). In one embodiment, the receiver, in addition to functions similar tothose previously described, may include decoding circuitry andprocessing to provide an estimation of transmitted signal on extendedconstellation associated to extended region to provide an extendeddecoded signal. The extended region may be an outward angular sectorwith a vertex being the original symbol location for the basicconstellation used as part of the demodulation, the outward angularregion defined by a value for an angle that forms a first boundary and asecond boundary for the outward angular region, the value for the anglebased on the constellation and a code rate for the stream of data.

The decoding and processing may also include the assigning of one ormore symbols from the estimation using the extended region to a symbolvalue based on symbol locations in the basic or non-extendedconstellation. The decoding and processing may be performed in ademapper used for processing all of the symbols in the received signal.The decoding circuitry, including the demapper, and processingassociated with the principles of the present disclosure may further beincluded in a demodulator (e.g., demodulator 124 described in FIG. 1),or in a channel decoder (e.g., channel decoder 123 described in FIG. 1),or in both.

In one embodiment, a receiver (e.g., receiver 120 described in FIG. 1)is adapted to receive signals transmitted using a transmission standardcompliant with ATSC 3.0. The signal includes at least of portion thathas been modulated using a 2D constellation and has been encoded using aforward error correction code rate such as is described earlier in Table2. The receiver decodes the received signal to provide an estimation ofat least one symbol in the transmitted signal on an extendedconstellation to provide an extended decoded signal, the extendedconstellation including at least on extended region formed as an outwardangular sector from an original location for a symbol in theconstellation, the outward angular region defined by a value for anangle forming a first boundary and a second boundary for the outwardangular region, the value for the angle based on the constellation andthe code rate for the stream of data. The value for the angle may be thevalue given in Table 2. Exemplary receivers capable of receiving ATSC3.0 signal may be included as part of televisions, set-top boxes,computers, gateways, mobile phones, mobile terminals, automobile radioreceivers, tablets, and the like.

The transmitted signal may also be received by a receiver employing MIMOsignal reception techniques (e.g, data receiver 400 described in FIG.4). The MIMO signal corresponds to a transmitted signal that has beenobtained by time or frequency mapping the input data on an extendedconstellation and on multiple carriers to generate a frequency domainsymbol per transmit antenna to generate multi-carrier signals andtransmission on a signal. The complex time or frequency de-mappingassociated with the MIMO signal may be carried out after projectiondecoding of the signal on the extended region constellation associatedto points of a corresponding basic constellation. The projectionincludes providing an estimate of the transmitted signal on the extendedconstellation associated to an extended region having an outward angularsector with a vertex being the original symbol location. The projectionmay also include initially assigning symbols in extended decoded signalto symbols of a basic or non-extended constellation, the outward angularregion defined by a value for an angle that forms a first boundary and asecond boundary for the outward angular region, the value for the anglebased on the constellation and a code rate for the stream of data. Theprojection decoding and processing may be performed in a separatedemapper used for processing the projected symbols in the receivedsignal. The projection decoding circuitry, including the demapper, andprocessing associated with the principles of the present disclosure mayfurther be included in a demodulator (e.g., OFDM demodulator 430 and 440described in FIG. 4), or in a time or frequency demapper (e.g.,time/frequency demapper 450 described in FIG. 4), or in both.

It is important to note that a receiver (e.g., receiver 120 described inFIG. 1 or data receiver 400 described in FIG. 4), and more particularlythe demapping and projection decoding circuitry and functions, must becapable of processing signals contained in the extended constellation.In order to improve the performance of the receiver, an additionallimiter circuit may be added to the receiver before any processingperformed by the demapper and/or projection decoding. The limitercircuit may limit or clip the amplitude of the signal. In oneembodiment, a scalar limiter may be added to limit or clip the amplitudein the x-axis and y-axis, often referred to as the in-phase (I) andquadrature (Q) axes. However, in a preferred embodiment using non-squareconstellations as part of the signal transmission, a complex modulusclipping circuit may be used in order to clip the signal as a vector.

The embodiments above describe various mechanisms and embodiments forprocessing a stream of input data into a signal containing aconstellation of OFDM symbols used for signal transmission in order toreduce the PAPR for the signal. The mechanisms may include processing orpre-encoding the data, represented as symbols in a constellation, toapply a constellation extension projection in a constellation to atleast one symbol, and modulating the pre-encoded signal to produce atransmitted signal, wherein the processing or pre-encoding applies aconstellation extension projection to the at least one symbol in anoutward angular sector using a vector based error signal. The boundariesproduced for the outward angular sector may be inherently non-orthogonaland are based on an angular distance between adjacent symbols or pointsin a constellation pattern. The outward angular region is defined by avalue for an angle between a first boundary and a second boundary forthe outward angular region, the value for the angle based on theconstellation and a signal stream encoding code rate, for instance afterFEC is applied, for the data. The angular sector used in theconstellation extension projection is more optimal particularly whenused in conjunction with non-square constellation patterns.

The present embodiments also apply to a data signal obtained by a methodas mentioned earlier. The present embodiments also apply to any decoderor decoding method adapted to decode this data signal. In particular, anembodiment applies to a data signal obtained from a method forprocessing a stream of data as part of transmitting the signal, themethod that includes pre-encoding the stream of data in order to reducepeak to average power ratio of the transmitted signal by applying asymbol constellation extension projection to at least one symbol in aconstellation used as part of a transmitted signal, the symbolconstellation extension projection having an outward angular region froman original position for the at least one symbol in the constellation,the outward angular region defined by a value for an angle between afirst boundary and a second boundary for the outward angular region, thevalue for the angle based on the constellation and a code rate for thestream of data. According to specific embodiments of the disclosure, themethod for processing a stream includes a terrestrial broadcasting ofthe data signal. According to specific embodiments of the disclosure,the data signal includes video and/or audio data. According to specificembodiments of the disclosure, the received or transmitted signalincludes or is a terrestrial broadcast signal.

The present embodiments describe a method for processing a stream ofdata converted into a plurality of symbols in a constellation as part oftransmitting a signal that includes applying a symbol constellationextension projection to at least one symbol in the constellation, thesymbol constellation extension projection having an outward angularregion from an original position for the at least one symbol in theconstellation, the outward angular region defined by a value for anangle between a first boundary and a second boundary for the outwardangular region, the value for the angle determined by a selection of theconstellation used as part of the transmitted signal and a code rateused for encoding the stream of data.

In some embodiments, the method may include the outward angular regionbeing formed between two boundary lines, the two boundary lines beingnon-orthogonal to each other.

In some embodiments, the method may include the angle between the twoboundary being equal to or less than the angle formed between aprojection line from an origin point in the constellation and the atleast one symbol and a projection line from the origin point in theconstellation and a symbol adjacent to the at least one symbol.

In some embodiments, the constellation may be at least one of a 16 QAMnon-square constellation, a 64-QAM non-square constellation, and a256-QAM non-square constellation.

In some embodiments, the constellation may be a non-uniformconstellation.

In some embodiments, the value for the angle may be based on theconstellation and the code rate values as given in Table 2 describedabove.

In some embodiments, the signal may comply with the Advanced TelevisionStandards Committee (ATSC) version 3.0 standard.

In some embodiments, the method may further include performing atransform on the signal, including the at least one symbol having thesymbol constellation extension projection, to produce a transformsignal, and modulating the pre-encoded transform signal to produce atransmitted signal.

In some embodiments, the applying may further include performing atransform on the stream of data to convert the stream of data to atransform domain signal, limiting the amplitude of the transform domainsignal to produce a clipped transform signal, performing an inversetransform on the clipped transform signal to produce an inversetransform signal, subtracting the stream of data from the inversetransform signal to produce a remainder signal, adjusting the signallevel of the remainder signal by a pre-determined gain factor to producean adjusted remainder signal, and adding the stream of data to theadjusted remainder signal to produce an error signal.

In some embodiments, the performing a transform or performing an inversetransform may use a Fourier transform.

In some embodiments, the method may be used as part of an orthogonalfrequency division multiplexing transmission.

In some embodiments, the method may be used as part of a two dimensionalactive constellation extension for the signal.

In some embodiments, an indication of the use of the two dimensionalactive constellation extension for the signal may be included in thetransmitted signal.

In some embodiments, the indication of use of the two dimensional activeconstellation extension for the signal may be included in L1 signalingportion of the transmitted signal.

In some embodiments, the processing of the stream of data is performedin order to reduce peak to average power ratio of the transmittedsignal.

The present embodiments also include an apparatus or portion thereofthat can be configured to perform any of the elements or steps of aprocess as described in one ore more of the preceding paragraphsdescribing a process or method for processing a stream of data convertedinto a plurality of symbols in a constellation as part of transmitting asignal.

The present embodiments also describe an apparatus for processing astream of data converted into a plurality of symbols in a constellationas part of transmitting a signal that includes a projection module, theprojection module applying a symbol constellation extension projectionto at least one symbol in the constellation, the symbol constellationextension projection having an outward angular region from an originalposition for the at least one symbol in the constellation, the outwardangular region defined by a value for an angle between a first boundaryand a second boundary for the outward angular region, the value for theangle determined by a selection of the constellation used as part of thetransmitted signal and a code rate for used for encoding the stream ofdata.

The present embodiments also include a method for processing a receivedsignal transmitted as a constellation of symbols representing a datastream that has been encoded using a code rate that includesdemodulating the received signal to provide an estimation of at leastone symbol in the transmitted signal on an extended constellation, theextended constellation including at least one extended region formed asan outward angular sector from an original location for a symbol in theconstellation, the outward angular region defined by a value for anangle between a first boundary and a second boundary for the outwardangular region, the value for the angle determined by a selection of theconstellation used as part of the transmitted signal and the code ratefor the data stream in the signal.

The present embodiments also describe an apparatus or portion thereoffor processing a received signal implementing the process described inthe preceding paragraph.

The present embodiments also describe an apparatus for processing areceived signal transmitted as a constellation of symbols representing adata stream that has been encoded using a code rate that includes ademodulator that demodulates the received signal to provide anestimation of at least one symbol in the transmitted signal on anextended constellation, the extended constellation including at leastone extended region formed as an outward angular sector from an originallocation for a symbol in the constellation, the outward angular regiondefined by a value for an angle between a first boundary and a secondboundary for the outward angular region, the value for the angledetermined by a selection of the constellation used as part of thetransmitted signal and the code rate for the data stream in the signal.

The present embodiments also describe a non-transitory device readablemedium containing instructions for processing a stream of data convertedinto a plurality of symbols in a constellation as part of transmitting asignal including applying a symbol constellation extension projection toat least one symbol in the constellation, the symbol constellationextension projection having an outward angular region from an originalposition for the at least one symbol in the constellation, the outwardangular region defined by a value for an angle between a first boundaryand a second boundary for the outward angular region, the value for theangle determined by a selection of the constellation used as part of thetransmitted signal and a code rate used for encoding the stream of data.

The present embodiments also describe a non-transitory device readablemedium containing instructions for processing a received signaltransmitted as a constellation of symbols representing a data streamthat has been encoded using a code rate including demodulating thereceived signal to provide an estimation of at least one symbol in thetransmitted signal on an extended constellation, the extendedconstellation including at least on extended region formed as an outwardangular sector from an original location for a symbol in theconstellation, the outward angular region defined by a value for anangle between a first boundary and a second boundary for the outwardangular region, the value for the angle determined by a selection of theconstellation used as part of the transmitted signal and the code ratefor the data stream in the signal.

The present embodiments also describe an electromagnetic signalincluding a processed stream of data converted into a plurality ofsymbols in a constellation, the electromagnetic signal processed byapplying a symbol constellation extension projection to at least onesymbol in the constellation, the symbol constellation extensionprojection having an outward angular region from an original positionfor the at least one symbol in the constellation, the outward angularregion defined by a value for an angle between a first boundary and asecond boundary for the outward angular region, the value for the angledetermined by a selection of the constellation used as part of thetransmitted signal and a code rate used for encoding the stream of data.

Although embodiments which incorporate the teachings of the presentdisclosure have been shown and described in detail herein, those skilledin the art can readily devise many other varied embodiments that stillincorporate these teachings. Having described preferred embodiments ofan apparatus and method for reducing peak to average power ratio in asignal (which are intended to be illustrative and not limiting), it isnoted that modifications and variations can be made by persons skilledin the art in light of the above teachings. It is therefore to beunderstood that changes may be made in the particular embodiments of thedisclosure disclosed which are within the scope of the disclosure asoutlined by the appended claims.

1-33. (canceled)
 34. A method for processing a stream of data convertedinto a plurality of symbols from a constellation as part of transmittinga signal, the method comprising: applying a symbol constellationextension projection to at least one symbol in the constellation, thesymbol constellation extension projection having an outward angularregion, the outward angular region defined by a value for an angle, thevalue for the angle determined by a selection of the constellation usedas part of the transmitted signal and a code rate used for encoding thestream of data, wherein the value for the angle based on theconstellation and the code rate equals the values given in the followingtable: Code Rate 2/ 3/ 4/ 5/ 6/ 7/ 8/ 9/ 10/ 11/ 12/ 13/ Constellation15 15 15 15 15 15 15 15 15 15 15 15 16QAM NA 33.26° 35.6° 38.5° 44.14°44.1° 44.49° 44.49° 42.1° NA NA NA 64QAM 22.96° 39.36° 41.26° 19.01°21.17° 22.49° 22.28° 22.49° 22.4° 19.75° 18.42° 16.81° 256QAM 36.67°40.26° 19.11° 22.47° 8.38° 11.23° 11.23° 10.93° 11.22° 10.63° 8.8° 8.34°


35. The method of claim 34, wherein the constellation is at least one ofa 16 QAM non-square constellation, a 64-QAM non-square constellation,and a 256-QAM non-square constellation.
 36. The method of claim 34,wherein the constellation is a non-uniform constellation.
 37. The methodof claim 34, wherein the signal complies with the Advanced TelevisionStandards Committee (ATSC) version 3.0 standard.
 38. The method of claim34, further comprising: performing a transform on the signal, includingthe at least one symbol having the symbol constellation extensionprojection, to produce a transform signal; and modulating the transformsignal to produce the transmitted signal.
 39. The method of claim 34,wherein the applying further includes: performing a transform on thestream of data to convert the stream of data to a transform domainsignal; limiting an amplitude of the transform domain signal to producea clipped transform signal; performing an inverse transform on theclipped transform signal to produce an inverse transform signal;subtracting the stream of data from the inverse transform signal toproduce a remainder signal; adjusting the signal level of the remaindersignal by a pre-determined gain factor to produce an adjusted remaindersignal; and adding the stream of data to the adjusted remainder signalto produce an error signal.
 40. The method of claim 34, wherein themethod is used as part of an orthogonal frequency division multiplexingtransmission.
 41. The method of claims 34, wherein an indication of useof a two dimensional active constellation extension for the signal isincluded in the transmitted signal.
 42. The method of claim 41, whereinthe indication of use of the two dimensional active constellationextension for the signal is included in an L1 signaling portion of thetransmitted signal.
 43. An apparatus for processing a stream of dataconverted into a plurality of symbols in a constellation as part oftransmitting a signal, comprising: a pre-encoder for applying a symbolconstellation extension projection to at least one symbol in theconstellation, the symbol constellation extension projection having anoutward angular region, the outward angular region defined by a valuefor an angle, the value for the angle determined by a selection of theconstellation used as part of the transmitted signal and a code rateused for encoding the stream of data, wherein the value for the anglebased on the constellation and the code rate equals the values given inthe following table: Code Rate 2/ 3/ 4/ 5/ 6/ 7/ 8/ 9/ 10/ 11/ 12/ 13/Constellation 15 15 15 15 15 15 15 15 15 15 15 15 16QAM NA 33.26° 35.6°38.5° 44.14° 44.1° 44.49° 44.49° 42.1° NA NA NA 64QAM 22.96° 39.36°41.26° 19.01° 21.17° 22.49° 22.28° 22.49° 22.4° 19.75° 18.42° 16.81°256QAM 36.67° 40.26° 19.11° 22.47° 8.38° 11.23° 11.23° 10.93° 11.22°10.63° 8.8° 8.34°


44. The apparatus of claim 43, wherein the constellation is at least oneof a 16 QAM non-square constellation, a 64-QAM non-square constellation,and a 256-QAM non-square constellation.
 45. The apparatus of claim 43,wherein the constellation is a non-uniform constellation.
 46. Theapparatus of claim 43, wherein the signal complies with the AdvancedTelevision Standards Committee (ATSC) version 3.0 standard.
 47. Theapparatus of claim 43, wherein the pre-encoder is further configured toperform a transform on the signal, including the at least one symbolhaving the symbol constellation extension projection, to produce atransform signal, the apparatus further including: a modulator formodulating the pre-encoded transform signal to produce the transmittedsignal.
 48. The apparatus of claim 43, wherein the pre-encoder isfurther configured to: perform a transform on the stream of data toconvert the stream of data to a transform domain signal, limit anamplitude of the transform domain signal to produce a clipped transformsignal, perform an inverse transform on the clipped transform signal toproduce an inverse transform signal, subtract the stream of data fromthe inverse transform signal to produce a remainder signal; adjust thesignal level of the remainder signal by a pre-determined gain factor toproduce an adjusted remainder signal, and add the stream of data to theadjusted remainder signal to produce an error signal.
 49. The apparatusof claim 43, wherein the apparatus is used as part of an orthogonalfrequency division multiplexing transmission.
 50. The apparatus of claim43, wherein an indication of use of a two dimensional activeconstellation extension for the signal is included in the transmittedsignal.
 51. The apparatus of claim 50, wherein the indication of use ofthe two dimensional active constellation extension for the signal isincluded in an L1 signaling portion of the transmitted signal.
 52. Amethod for processing a received signal transmitted as a constellationof symbols representing a data stream, the method comprising:demodulating the received signal to provide an estimation of at leastone symbol in the transmitted signal on an extended constellation, theextended constellation including at least one extended region formed asan outward angular region, the outward angular region defined by a valuefor an angle, the value for the angle determined by a selection of theconstellation used as part of the transmitted signal and a code rate forthe data stream in the transmitted signal, wherein the value for theangle based on the constellation and the code rate equals the valuesgiven in the following table: Code Rate 2/ 3/ 4/ 5/ 6/ 7/ 8/ 9/ 10/ 11/12/ 13/ Constellation 15 15 15 15 15 15 15 15 15 15 15 15 16QAM NA33.26° 35.6° 38.5° 44.14° 44.1° 44.49° 44.49° 42.1° NA NA NA 64QAM22.96° 39.36° 41.26° 19.01° 21.17° 22.49° 22.28° 22.49° 22.4° 19.75°18.42° 16.81° 256QAM 36.67° 40.26° 19.11° 22.47° 8.38° 11.23° 11.23°10.93° 11.22° 10.63° 8.8° 8.34°


53. The method of claim 52, wherein the constellation is at least one ofa 16 QAM non-square constellation, a 64-QAM non-square constellation,and a 256-QAM non-square constellation.
 54. The method of claim 52,wherein the constellation is a non-uniform constellation.
 55. The methodof claim 52, wherein the signal complies with the Advanced TelevisionStandards Committee (ATSC) version 3.0 standard.
 56. The method of claim52, wherein a signal modulation is orthogonal frequency divisionmultiplexing.
 57. The method of claim 52, wherein an indication of useof a two dimensional active constellation extension for the signal isincluded in the received signal.
 58. The method of claim 52, wherein theindication of use of the two dimensional active constellation extensionfor the signal is included in L1 signaling portion of the receivedsignal.
 59. An apparatus for processing a received signal transmitted asa constellation of symbols representing a data stream that has beenencoded using a code rate, the apparatus comprising: a demodulator fordemodulating the received signal to provide an estimation of at leastone symbol in the transmitted signal on an extended constellation, theextended constellation including at least one extended region formed asan outward angular region, the outward angular region defined by a valuefor an angle, the value for the angle determined by a selection of theconstellation used as part of the transmitted signal and the code ratefor the data stream in the transmitted signal, wherein the value for theangle based on the constellation and the code rate equals the valuesgiven in the following table: Code Rate 2/ 3/ 4/ 5/ 6/ 7/ 8/ 9/ 10/ 11/12/ 13/ Constellation 15 15 15 15 15 15 15 15 15 15 15 15 16QAM NA33.26° 35.6° 38.5° 44.14° 44.1° 44.49° 44.49° 42.1° NA NA NA 64QAM22.96° 39.36° 41.26° 19.01° 21.17° 22.49° 22.28° 22.49° 22.4° 19.75°18.42° 16.81° 256QAM 36.67° 40.26° 19.11° 22.47° 8.38° 11.23° 11.23°10.93° 11.22° 10.63° 8.8° 8.34°


60. The apparatus of claim 59, wherein the constellation is at least oneof a 16 QAM non-square constellation, a 64-QAM non-square constellation,and a 256-QAM non-square constellation.
 61. The apparatus of claim 59,wherein the constellation is a non-uniform constellation.
 62. Theapparatus of claim 59, wherein the signal complies with the AdvancedTelevision Standards Committee (ATSC) version 3.0 standard.
 63. Theapparatus of claim 59, wherein a signal modulation is orthogonalfrequency division multiplexing.
 64. The apparatus of claim 59, whereinan indication of use of a two dimensional active constellation extensionfor the signal is included in the received signal.
 65. The apparatus ofclaim 59, wherein the indication of use of the two dimensional activeconstellation extension for the signal is included in L1 signalingportion of the received signal.
 66. A non-transitory device readablemedium containing instructions for processing a received signaltransmitted as a constellation of symbols representing a data stream,comprising: demodulating the received signal to provide an estimation ofat least one symbol in the transmitted signal on an extendedconstellation, the extended constellation including at least on extendedregion formed as an outward angular region, the outward angular regiondefined by a value for an angle, the value for the angle determined by aselection of the constellation used as part of the transmitted signaland the code rate for the data stream in the transmitted signal, whereinthe value for the angle based on the constellation and the code rateequals the values given in the following table: Code Rate 2/ 3/ 4/ 5/ 6/7/ 8/ 9/ 10/ 11/ 12/ 13/ Constellation 15 15 15 15 15 15 15 15 15 15 1515 16QAM NA 33.26° 35.6° 38.5° 44.14° 44.1° 44.49° 44.49° 42.1° NA NA NA64QAM 22.96° 39.36° 41.26° 19.01° 21.17° 22.49° 22.28° 22.49° 22.4°19.75° 18.42° 16.81° 256QAM 36.67° 40.26° 19.11° 22.47° 8.38° 11.23°11.23° 10.93° 11.22° 10.63° 8.8° 8.34°